Add

In VB.NET programs, we can sometimes create and use Lists with all their elements initialized at once. But usually we must call Add() to place more elements at the end.

With List Add, we must pass an argument of the correct type, and it is added to the end (appended) to the List. We can use Add() with Integers, Strings, and even custom Class instances.

Integer example

Consider this first example—we want a List of prime numbers. We represent these prime numbers as Integers, and use Add() to append them to the List.

Step 1 We create the List generic collection, and then call Add() 4 times to add the first 4 prime numbers.

Step 2 We use a For Each loop over the list to display the elements with in. We call Console.WriteLine.

Module Module1

    Sub Main()
        ' Step 1: add some primes to the list.
        Dim list = New List(Of Integer)
        list.Add(2)
        list.Add(3)
        list.Add(5)
        list.Add(7)

        ' Step 2: print all the primes in the list.
        For Each value in list
            Console.WriteLine(value)
        Next
    End Sub

End Module2
3
5
7

`Class` example

Consider this example, where we specify a custom Class with 2 fields in it. We then create Class instances and pass them to Add.

Step 1 We create a new List. We specify the type Test to indicate we want Test objects in the list.

Step 2 We call Add() 3 times, and in each call, we create a new Test instance by invoking the New function.

Step 3 After calling Add 3 times, we have 3 objects in the List, and we can use them in any way.

Module Module1

    Class Test
        Private _a as Integer
        Private _b as Integer
        Public Sub New(a as Integer, b as Integer)
            _a = a
            _b = b
        End Sub
    End Class

    Sub Main()
        ' Step 1: create new List.
        Dim list = New List(Of Test)

        ' Step 2: invoke the Add method 3 times and create objects to place in the list.
        list.Add(New Test(1, 2))
        list.Add(New Test(3, 4))
        list.Add(New Test(5, 6))

        ' Step 3: there are now 3 objects in the list.
        Console.WriteLine("DONE: {0}", list.Count)
    End Sub
End Module
DONE: 3

Summary

It is possible to append elements to a List any time after it was created. Lists are designed to grow their capacity as needed, so Add() is almost always safe to call.

Add

Integer example

Class example

Summary

`Class` example